1. Field of the Invention
The present invention relates to a bending tool mounted on a press bending machine (also called a press brake) for bending machanical parts.
2. Description of the Prior Art
Various types of L- or Z-shaped fittings are widely used as brackets and reinforcing members for structures of machines and equipments. These L- or Z-shaped fittings are manufactured by bending tools, and an example of improvement over conventional bending tools may be found in the U.S. Pat. No. 4,356,718 or in FIG. 1. FIG. 1 schematically shows the side view of a bending tool consisting of a pair of an upper die 7 and a lower die 17. The upper die 7 is securely fixed at its base to a body 9 of the press bending machine by means of bolts 10 or other suitable fastening means.
Disposed beneath the upper die 7 is the lower die 17 which is securely fixed to a table 22 of the press bending machine body 9 by screws 23.
The upper die 7 consists of a blade 3 and a bending block 6. The blade 3 has a pointed edge with a bending angle of about 90.degree., arranged so that a vertical center line of the edge bisects the bending angle. The edge, in cross section, has a longer side 1 on the outside with respect to the vertical center line and a shorter side 2 on the inside. The bending block 6 is laterally or horizontally spaced from the short edge side 2 of the blade 3 with an adjustable gap 5 therebetween, and has a nearly rectangular end face 4 opposing the shorter edge side 2 of the blade 3. The end face 4 of the bending block 6 and the blade 3 define the adjustable gap 5 which is rectangular in cross section, cutting into the upper die perpendicularly from the bottom end surface of the upper die. The bending block 6 is securely mounted to the body of the upper die 7 by screws 21 or other fastening means. Inserted between the bending block 6 and the die body that supports the bending block are a plurality of thin plate-like spacers 20, the number of which is increased or reduced to adjust the size of the gap 5.
The lower die 17 has a similar construction to the upper die 7. That is, the lower die 17 consists of a blade 13 and a bending block 16. The blade 13 has a pointed edge with a bending angle of about 90.degree., arranged so that a vertical center line of the edge bisects the bending angle. The edge, in cross section, has a longer side 11 on the outside with respect to the vertical center line and a shorter side 12 on the inner side. The bending block 6 is laterally spaced from the shorter edge side 12 of the blade 13 with an adjustable gap 15 therebetween, and has a nearly rectangular end face 14 opposing the shorter edge side 12 of the blade 13. The end face 14 of the bending block 16 and the blade 13 define the adjustable gap 15 which is rectangular in cross section, cutting into the lower die perpendicularly from the top end surface of the lower die. The bending block 16 is securely mounted to the body of the lower die 17 by screws 19 or other fastening means. Inserted between the bending block 16 and the die body that supports the bending block are spacers 19, the number of which is increased or reduced to adjust the size of the gap 15.
The upper die 7 and the lower die 17 are disposed to oppose each other in such a way that the center line of the blade of one die comes almost at the center between the blade center line of the other die and the end face of the bending block of the latter die facing the blade. In this positional relationship, the two dies 7, 17 are mounted to the body 9 of the bending machine and vertically moved toward and away from each other. As a result, the upper and lower dies 7, 17 engage with each other, bending a work 24 placed on the lower die 17 into a Z-shaped section.
Such conventional bending tools for press bending machines, however, have the following drawbacks. Since the gap 5 is formed between the blade 3 and the bending block mount 25, and since the blade and the bending block mount are formed integral with the body of the upper die 7, it is difficult to form corner portions 26, 27 on each side of the gap 5 perfectly rectangular. Particularly when the corner portion 27 is not formed rectangular with precision, the bending block 6 and spacers 20, when mounted on the end surface of the bending block mount 25, will incline, rendering the bending of the work 24 innacurate. The same also applies to the lower die 17. Since the corner portions 29, 30 between the blade 13 and the bending block mount 28 are difficult to form at right angles with accuracy, the bending block 16 and the spacers 18 tend to be mounted tilted.